Secure telephone

Last updated June 11, 2022

A Secure Terminal Equipment desk set. STE telephone.nsa.jpg — A Secure Terminal Equipment desk set.

A secure telephone is a telephone that provides voice security in the form of end-to-end encryption for the telephone call, and in some cases also the mutual authentication of the call parties, protecting them against a man-in-the-middle attack. Concerns about massive growth of telephone tapping incidents led to growing demand for secure telephones.

Well-known products

The best-known product on the US government market is the STU-III family. However, this system has now been replaced by the Secure Terminal Equipment (STE) and SCIP standards which defines specifications for the design of equipment to secure both data and voice. The SCIP standard was developed by the NSA and the US DOD to derive more interoperability between secure communication equipment. A new family of standard secure phones has been developed based on Philip Zimmermann's VoIP encryption standard ZRTP.^[1]

VoIP and direct connection phones

As the popularity of VoIP grows, secure telephony is becoming more widely used. Many major hardware and software providers offer it as a standard feature at no extra cost.

Examples include the Gizmo5 and Twinkle. Both of the former work with offerings from the founder of PGP, Phil Zimmermann, and his VoIP secure protocol, ZRTP. ZRTP is implemented in, amongst others, Ripcord Networks product SecurePC with up to NSA Suite B compliant Elliptic Curve math libraries. ZRTP is also being made available for mobile GSM CSD as a new standard for non-VoIP secure calls.

The U.S. National Security Agency is developing a secure phone based on Google's Android called Fishbowl.

Historically significant products

SIGSALY exhibit at the National Cryptologic Museum SIGSALY.jpg — SIGSALY exhibit at the National Cryptologic Museum

Scramblers were used to secure voice traffic during World War II, but were often intercepted and decoded due to scrambling's inherent insecurity. The first true secure telephone was SIGSALY, a massive device that weighed over 50 tons. The NSA, formed after World War II, developed a series of secure telephones, including the STU I, STU II and STU-III, as well as voice encryption devices for military telephones.

In 1989 an Irish company called Intrepid developed one of the most advanced secure phones. Called Milcode, the phone was the first to implement code-excited linear prediction (or CELP) which dramatically improved voice quality and user operability over previous LPC (Linear Predictive Coding) and LPC-10e versions.

Milcode also boasted significantly higher levels of security than previous secure telephones. The base model offered a proprietary encryption algorithm with a key length of 512 bits, and a more advanced model with a key length of 1024 bits. Key exchange used a public key, based on Diffie-Hellman, as opposed to a plug-in datakey. A new key was generated for each phone call. Milcode was also able to encrypt fax and data and was electromagnetically shielded to NATO TEMPEST standards.

Other products of historical significance are PGPfone and Nautilus (designed as a non-key escrow alternative to Clipper, now officially discontinued, but still available on SourceForge), SpeakFreely, and the security VoIP protocol wrapper Zfone developed by the creator of PGP.

Scrambling, generally using a form of voice inversion, was available from electronic hobbyist kit suppliers and is common on FRS radios. Analog scrambling is still used, as some telecommunications circuits, such as HF links and telephone lines in the developing world, are of very low quality.

Related Research Articles

Philip R. Zimmermann is an American computer scientist and cryptographer. He is the creator of Pretty Good Privacy (PGP), the most widely used email encryption software in the world. He is also known for his work in VoIP encryption protocols, notably ZRTP and Zfone. Zimmermann is co-founder and Chief Scientist of the global encrypted communications firm Silent Circle.

Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet telephony, broadband telephony, and broadband phone service specifically refer to the provisioning of communications services over the Internet, rather than via the public switched telephone network (PSTN), also known as plain old telephone service (POTS).

The Clipper chip was a chipset that was developed and promoted by the United States National Security Agency (NSA) as an encryption device that secured "voice and data messages" with a built-in backdoor that was intended to "allow Federal, State, and local law enforcement officials the ability to decode intercepted voice and data transmissions." It was intended to be adopted by telecommunications companies for voice transmission. Introduced in 1993, it was entirely defunct by 1996.

There are a number of standards related to cryptography. Standard algorithms and protocols provide a focus for study; standards for popular applications attract a large amount of cryptanalysis.

STU-III is a family of secure telephones introduced in 1987 by the NSA for use by the United States government, its contractors, and its allies. STU-III desk units look much like typical office telephones, plug into a standard telephone wall jack and can make calls to any ordinary phone user. When a call is placed to another STU-III unit that is properly set up, one caller can ask the other to initiate secure transmission. They then press a button on their telephones and, after a 15-second delay, their call is encrypted to prevent eavesdropping. There are portable and militarized versions and most STU-IIIs contained an internal modem and RS-232 port for data and fax transmission. Vendors were AT&T, RCA and Motorola.

Secure Terminal Equipment Encrypted telephone system

Secure Terminal Equipment (STE) is the U.S. government's current, encrypted telephone communications system for wired or "landline" communications. STE is designed to use ISDN telephone lines which offer higher speeds of up to 128 kbit/s and are all digital. The greater bandwidth allows higher quality voice and can also be utilized for data and fax transmission through a built-in RS-232 port. STE is intended to replace the older STU-III office system and the KY-68 tactical system. STE sets are backwards compatible with STU-III phones, but not with KY-68 sets.

The National Security Agency took over responsibility for all U.S. Government encryption systems when it was formed in 1952. The technical details of most NSA-approved systems are still classified, but much more about its early systems have become known and its most modern systems share at least some features with commercial products.

The Secure Communications Interoperability Protocol (SCIP) is a US standard for secure voice and data communication, for circuit-switched one-to-one connections, not packet-switched networks. SCIP derived from the US Government Future Narrowband Digital Terminal (FNBDT) project. SCIP supports a number of different modes, including national and multinational modes which employ different cryptography. Many nations and industries develop SCIP devices to support the multinational and national modes of SCIP.

Secure voice is a term in cryptography for the encryption of voice communication over a range of communication types such as radio, telephone or IP.

PGPfone was a secure voice telephony system developed by Philip Zimmermann in 1995. The PGPfone protocol had little in common with Zimmermann's popular PGP email encryption package, except for the use of the name. It used ephemeral Diffie-Hellman protocol to establish a session key, which was then used to encrypt the stream of voice packets. The two parties compared a short authentication string to detect a Man-in-the-middle attack, which is the most common method of wiretapping secure phones of this type. PGPfone could be used point-to-point over the public switched telephone network, or over the Internet as an early Voice over IP system.

OMNI is an encryption device manufactured by L-3 Communications. It adds secure voice and secure data to any standard analog telephone or modem connected computer.

Opportunistic encryption (OE) refers to any system that, when connecting to another system, attempts to encrypt communications channels, otherwise falling back to unencrypted communications. This method requires no pre-arrangement between the two systems.

The STU-II is a secure telephone developed by the U.S. National Security Agency. It permitted up to six users to have secure communications, on a time-shared basis. It was made by ITT Defense Communications, Nutley, New Jersey. An OEM partner was Northern Telecom.

Zfone is software for secure voice communication over the Internet (VoIP), using the ZRTP protocol. It is created by Phil Zimmermann, the creator of the PGP encryption software. Zfone works on top of existing SIP- and RTP-programs, but should work with any SIP- and RTP-compliant VoIP-program.

ZRTP is a cryptographic key-agreement protocol to negotiate the keys for encryption between two end points in a Voice over IP (VoIP) phone telephony call based on the Real-time Transport Protocol. It uses Diffie–Hellman key exchange and the Secure Real-time Transport Protocol (SRTP) for encryption. ZRTP was developed by Phil Zimmermann, with help from Bryce Wilcox-O'Hearn, Colin Plumb, Jon Callas and Alan Johnston and was submitted to the Internet Engineering Task Force (IETF) by Zimmermann, Callas and Johnston on March 5, 2006 and published on April 11, 2011 as RFC 6189.

This is a comparison of voice over IP (VoIP) software used to conduct telephone-like voice conversations across Internet Protocol (IP) based networks. For residential markets, voice over IP phone service is often cheaper than traditional public switched telephone network (PSTN) service and can remove geographic restrictions to telephone numbers, e.g., have a PSTN phone number in a New York area code ring in Tokyo.

A VoIP VPN combines voice over IP and virtual private network technologies to offer a method for delivering secure voice. Because VoIP transmits digitized voice as a stream of data, the VoIP VPN solution accomplishes voice encryption quite simply, applying standard data-encryption mechanisms inherently available in the collection of protocols used to implement a VPN.

The 1100-series IP phones are 6 different desktop IP clients manufactured by Avaya for Unified communications which can operate on the SIP or UNIStim protocols. The SIP Firmware supports presence selection and notification along with secure instant messaging.

Acrobits is a privately owned software development company creating VoIP Clients for mobile platforms, based in Prague, Czech Republic.

References

↑ Aboraya, Ahmed; Nasrallah, Henry; Muvvala, Srinivas; El-Missiry, Ahmed; Mansour, Hader; Hill, Cheryl; Elswick, Daniel; Price, Elizabeth C. (May 2016). "The Standard for Clinicians' Interview in Psychiatry (SCIP): A Clinician-administered Tool with Categorical, Dimensional, and Numeric Output-Conceptual Development, Design, and Description of the SCIP". Innovations in Clinical Neuroscience. 13 (5–6): 31–77. ISSN 2158-8333. PMC 5077257 . PMID 27800284.

External links

Seminar on crypto phones by Zidu Wang

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[1] Aboraya, Ahmed; Nasrallah, Henry; Muvvala, Srinivas; El-Missiry, Ahmed; Mansour, Hader; Hill, Cheryl; Elswick, Daniel; Price, Elizabeth C. (May 2016). "The Standard for Clinicians' Interview in Psychiatry (SCIP): A Clinician-administered Tool with Categorical, Dimensional, and Numeric Output-Conceptual Development, Design, and Description of the SCIP". Innovations in Clinical Neuroscience. 13 (5–6): 31–77. ISSN 2158-8333. PMC 5077257 . PMID 27800284.

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